88 C. RiMINGTON 



inhibitors, but in no case was significant interference with 

 ^^N incorporation demonstrable. The substances used were: — 



Sodium fluoride 10-^ molar final concentration. 



Sodium iodoacetate 10"* molar final concentration (possibly 



a slight depression). 

 Sodium malonate 10'^ molar final concentration. 



2:4-dinitrophenol (10"^ molar) used to "uncouple" phos- 

 phorylation processes, was similarly ineffective with or with- 

 out added glucose. 



It would appear therefore either that the inhibitors used 

 did not penetrate in sufficient concentration to the enzyme 

 system providing energy for synthesis from glucose meta- 

 bolism, or that haem synthesis derives energy from sources 

 other than carbohydrate metabolism. 



That permeability was the limiting factor seems unlikely 

 in view of the fact that these same substances behave as 

 effective inhibitors of the intracorpuscular reduction of 

 methaemoglobin to haemoglobin, a process which is believed 

 on good evidence (Kiese and Schwartzkopf, 1947) to be linked 

 with the metabolism of carbohydrate within the cell. We are 

 doing further work upon this problem. 



Another observation which I would like to mention is that 

 the biosynthesis of hgem by this isolated red cell system can 

 be markedly inhibited by addition of lead salts (Table III). 



Table III 



Inhibitory Action of Pb Acetate on H^m Synthesis by Fowl 



Erythrocytes 



